Question

Why the number of ATP is not known exactly?

Answer 1

ATP:

1. Adenosine triphosphate (ATP) is the primary source of energy for all living beings.
2. Structurally ATP is a nucleoside triphosphate, that consists of a nitrogenous base (adenine), a ribose sugar, and three sequentially bonded phosphate groups.
3. It is also known as the energy currency of the cell.

The number of ATP is not known exactly because:

1. The number of ATP generation depends upon the flow of protons through ATPase and electron transport.
2. Any variance in the degree of coupling between the flow of protons through the ATPase and electron transport will affect the number of ATPs synthesised.

Electron transport:

1. It can be defined as a sequence of redox reactions.
2. It is a part of aerobic respiration.
3. It is the only part of glucose metabolism where atmospheric oxygen is used.
4. When electrons are passed from one component to another till they reach the end of the chain, the electrons reduce molecular oxygen and produce water.
5. The requirement of oxygen in the final stage can be seen in the chemical reaction that includes the requirement of both oxygen and glucose.

Electron transport chain in mitochondria:

A complex can be defined as a structure that consists of a weak protein molecule or atom which is weakly connected to a protein. The plasma membrane of prokaryotic organisms consists of multiple copies of the electron transport chain.

Complex 1- NADH-Q oxidoreductase:

1. It consists of enzymes comprising iron-sulfur and FMN (Flavin mononucleotide).
2. Here two electrons are brought out to the first complex i.e NADH.
3. FMN is derived from vitamin B2.

Q and Complex 2- Succinate-Q reductase:

1. FADH2 that does not pass through complex 1 is taken up by complex 2 directly.
2. The first and the second complexes are connected to a third complex through the compound ubiquinone (Q).
3. The Q molecule is water soluble and can move freely in the hydrophobic core of the membrane.
4. In this stage, an electron is provided directly to the electron protein chain.
5. The number of ATP obtained at this stage is directly proportional to the number of protons that are pumped across the inner membrane of the mitochondria.

Complex 3- Cytochrome c reductase:

1. The third complex is formed of Fe-S protein, Cytochrome-b, and Cytochrome-c proteins.
2. Cytochrome proteins include the heme group.
3. Complex 3 pumps protons across the membrane.
4. It also passes electrons to the cytochrome c where they are transported to the 4th complex of enzymes and proteins.
5. Here, Q serves as the electron donor and Cytochrome C is the electron acceptor.

Complex 4- Cytochrome c oxidase:

1. The 4th complex conssits of cytochrome c, a and a3.
2. There are two heme groups and each of them is present in cytochromes c and a3.
3. The cytochromes hold oxygen molecules between copper and iron until the oxygen content is reduced completely.
4. In this phase, the reduced oxygen combines with two hydrogen ions from the surroundings and forms water.